The protein component of the iron storage molecule, ferritin, contains 24 subunits in form of a hollow shell known as apoferritin. The amino acid sequence has been determined for apoferritin subunits from human liver. The sequence comprises 174 amino acids giving an it4* of 19 900. It shows extensive homology with the primary structures of apoferritins from human and horse spleen and from rat Iiver. Sequence substitutions are discussed in relation to the known three-dimensional structure of horse spleen apoferritin.Evidence for a second minor sequence in human liver apoferritin is presented. Human liver upoferritin